In this chapter, a study on two kinds of examples of functional nanofibers has been introduced. In the first section, the formation of nanofiber morphology at a mesoscopic scale and molecular level stacking of a tetrathiafulvalene (TTF) derivative with a chiral group were investigated by the one-dimensional growth method in interfacial molecular films. Monomolecular films of a TTF derivative with a chiral borneol group display a two-dimensional phase transition at the air/water interface. The formation of nanonetwork domains is attributed to the organized aggregation of the TTF derivatives, which is a result of strong intermolecular interactions. In the second section, the formation of nanofiber morphology at a mesoscopic scale and molecular level packing of an amphiphilic diamide derivative with two hydrocarbons were investigated by the in interfacial molecular films. It has found that the growth of this nanofiber morphology is encouraged by the application of the epitaxial growth in the spin-cast film with 1 wt% layered silicate having long hydrocarbons. As mention above, it is found that mesoscopic morphological formation of super-hierarchical structure of the nanofibers having a crystalline arrangement at Å level can be induced conductivity and the thixotropy at macroscopic level.
- crystalline nanofiber
- TTF derivative
- diamide derivative with two hydrocarbons
- thixotropic ability
- one-dimensional growth
1. Morphological transition of a conductive molecular organization with non-covalent from nanonetwork to nanofiber
Although the synthesis of the Langmuir–Blodgett (LB) film was first reported by Blodgett in 1934 , this technique has attracted a lot of attention in recent years, following its application in the formation of two-dimensional lamellae in linear polymers . While there is a long history of development of this technique beginning with the studies on the optical and electronic properties of the LB films by Khun et al. [3, 4], direct observation of the folding of polymer chains in LB films using atomic force microscopy was a significant milestone, which revealed the phenomenon of “morphogenesis at the interface” [5, 6]. For the several examples of “morphogenesis at the interface,” the formation of nanofibers , nanowires [8, 9], nanospheres , nanocoils , nanoribbons , sea-island structures [13, 14], rods , gyroids , lamellae , and honeycombs  are noteworthy. Simultaneous control of the mesoscopic morphology (at the sub-micron level) of a non-covalent molecular organization, along with control of the molecular arrangement and packing structure (at the sub-nanometer level), is essential for the construction of next-generation quantum devices and medical materials. In other words, the molecular arrangement and morphology need to be controlled at different dimensional scales.
In this chapter, the formation of a nanofiber morphology at the mesoscopic scale and the molecular level stacking of a tetrathiafulvalene (TTF) derivative with a chiral group were investigated by the method of one-dimensional molecular film growth (Figure 1(a)). The fabrication of a nanometer-scale thin film having a fibril texture, which was achieved by incorporating a phenyl group in the TTF derivatives, has been reported previously . However, the strong interactions between the molecules, which is a consequence of the competing forces of π–π interactions (of TTFs and phenyl rings) and hydrogen-bonding (of urethane bonding units), inhibited accurate morphological control. Therefore, in our previous study, we attempted to substitute the phenyl ring with the bulky and chiral borneol group , in order to minimize these strong intermolecular interactions. However, since TTF derivatives containing borneol groups are amorphous, top-down fabrication of thin films and control of the molecular arrangement were quite difficult.
Organized molecular films  have been developed as potential candidates for the synthesis of biomimetic models  and molecular electronic devices [23, 24], which are of considerable technological interest [25–29]. In addition to the interaction of lipids and proteins with hydrocarbons, various amphiphiles containing functional groups (including π- and
In the present chapter, a new, conducting, four-armed amphiphilic compound (a TTF derivative with chiral borneol groups (TTF-4Bor, Figure 1(b) ) was synthesized. The monolayer behavior, molecular arrangement, and surface morphology of organized molecular films of TTF-4Bor were investigated by analysis of the surface pressure–area (π–A) isotherms, in-plane and out-of-plane X-ray diffraction (XRD) profiles, and atomic force microscopy (AFM) images. Further, morphogenesis was encouraged by applying the one-dimensional growth method to an LB film of TTF-4Bor in distilled water, under low surface pressure conditions. The size of the nanofibers thus obtained was controlled by variation of the subphase temperature. Since the internal structure of the mesoscopic nanofiber is comprised of stacked TTF planes at a molecular level, effective electrical conduction is expected along the direction of stacking.
1.2. Experimental section
1.2.1. Synthesis of TTF-4Bor (Scheme S1)
A three-necked flask with a stirrer was purged with nitrogen, followed by the addition of L(-)-borneol (compound
1.2.2. Formation of monolayers of TTF-4Bor on the water surface
Monolayers were formed by spreading a toluene solution of TTF-4Bor (∼1.0 × 10−4 M) on the surface of distilled water (resistivity: approximately 18.2 MΩ cm). After evaporation of the toluene for 5 min, surface pressure–area (π–A) isotherms were recorded at compression speeds ranging from 0.8 to 4.8 cm2 min−1. The air/water interface was kept at a constant temperature of 15°C by circulation of thermostated water around the trough. Measurement of the monolayer properties and LB film transfer were carried out in a USI-3-22 Teflon-coated LB trough (USI Instruments).
1.2.3. Study of the surface morphology and estimation of the molecular arrangement
The surface morphologies of the transferred films were observed using a scanning probe microscope (Atomic Force Microscopy, SII Nanotechnology, SPA300 with SPI-3800 probe station), and microfabricated rectangular Si cantilevers with integrated pyramidal tips, by applying a constant force of 1.4 N m−1. In this chapter, AFM observations were carried out in the tapping mode. XRD samples were transferred onto a glass substrate by the LB method (20 layers, subphase temperature of 15°C, and surface pressures of 5 and 35 mN m−1). The large spacing between the layers in the films was measured using an out-of-plane X-ray diffractometer (Rigaku, Rint-Ultima III, CuKα radiation, 40 kV, 30 mA) equipped with a graphite monochromator. The in-plane spacing of the two-dimensional lattice of the films was determined using an X-ray diffractometer with different geometrical arrangements [31, 32] (Bruker AXS, MXP-BX, CuKα radiation, 40 kV, 40 mA, a customized instrument) and equipped with a parabolic-graded multilayer mirror. The X-rays were incident at an angle of 0.2°, and the films were scanned at a speed of 0.05°/80 s, as a result of which the in-plane XRD measurements had monomolecular resolution.
1.3. Results and discussion
1.3.1. Monolayer behavior and surface morphology of TTF-4Bor
Figure 2 shows the π–
Figure 3 shows the AFM images of LB monolayers of TTF-4Bor (Z-type) on mica, transferred at 35 and 10 mN m−1. At low surface pressures, sparsely dotted nanodomains with a height of about 1 nm are observed, confirming the flat-on orientation of the molecular planes. In the high pressure regions, however, submicron network domains are formed, and the height information indicates that the conformation of the TTF derivatives is normal to the plane of the film. It has been suggested that the mesoscopic morphogenesis is attained by aggregation, which is based on the competition between the π–π interaction of the TTF molecular planes, and the strong interaction of hydrogen bonds between the urethane bonding sites. This hypothesis is supported by the infrared (IR) spectra (Figure 3(c)), which exhibit a shift of the band attributed to the carbonyl group toward lower wavenumbers, indicating the formation of hydrogen bonds [19, 20].
1.3.2. Molecular arrangement in organized molecular films of TTF-4Bor
In order to estimate the crystallinity and periodicity of the molecules in multilayers of TTF-4Bor, in-plane and out-of-plane XRD analyses of LB multilayers were carried out. In-plane XRD profiles of multilayers transferred at 35 and 10 mN m−1 are shown in Figure 4. This technique provides information regarding molecular arrangement at a sub-nanometer scale, and the internal fine structure of the mesoscopic morphology. At low surface pressures, a clear periodic structure was not observed, indicating that the film might be amorphous. On the other hand, in the LB multilayers formed at high surface pressures, a clear periodic structure with regular molecular packing was confirmed. The short spacing value of 4.1 Å appears to correspond to the stacking of the TTF molecular planes based on π–π interactions. A similar in-plane packing system based on π–π interactions, established by in-plane XRD, was reported in conducting organized molecular films of metal (dmit)2 charge transfer complexes . Dense stacking of molecular planes has been known to induce electrical conductivity along the direction of stacking.
Figure 5 shows the out-of-plane XRD profiles for LB multilayers (20 layers) of TTF-4Bor, transferred at 35 and 10 mN m−1. In the multilayers fabricated under high surface pressure conditions, a
1.3.3. Morphological changes from a two-dimensional film to nanofibers of TTF-4Bor
At present, there are limitations in the ability to achieve one-dimensional growth of a nanofiber consisting of tightly stacked electrically conducting molecules. Although stacked conducting molecular planes are obtained at high surface pressures, morphologies at the mesoscopic scale are too developed due to the strong forces of aggregation, with the presence of long-range order between molecules, as a result of the competitive effect of π–π interactions and hydrogen bonding. Hence, although the molecules cannot be arranged under low surface pressure conditions, the disordered molecular groups can be rearranged by multilayer formation, owing to their strong aggregation tendency. In this chapter, the technique of one-dimensional growth at the air/water interface was adopted, which involved transfer of the film at low surface pressures with reduction of the compression speed (by a factor of 8), inducing a spontaneous growth structure at the interface. Figure 7 shows a comparison of the π–A isotherms, at different compression speeds (4.8 and 0.6 cm2 min−1), and a schematic illustration of molecular aggregation. The tendency to expand at low pressures and condense at higher pressures is conspicuous in the π–A isotherms measured at a low compression rate (0.6 cm2 min−1).
In Figure 8, AFM images of the Z-type monolayers of TTF-4Bor after one-dimensional growth are shown, along with the in-plane XRD profiles of multilayers of TTF-4Bor transferred at 10 mN m−1 with a compression speed of 0.6 cm2 min−1. In this system, there is a clear transition from a mesoscopic morphology to a nanofiber shape (thickness ∼70 nm). While many of the nanofibers are linear (Figure 8(a)), some fibers exhibit a branching morphology (Figure 8(b)) and some others grew as a right-handed spiral. This morphological formation is expected to have occurred to minimize the steric hindrance from the four functional groups in the TTF derivative. This material exhibited circular dichroism (CD) for every adsorption band , and the Cotton effect centered around 380 and 530 nm was attributed to the helical dipole coupling between TTF rings through the formation of a network of hydrogen bonds [34–38]. In-plane XRD reveals multilayers of these integrated nanofiber films, with the formation of stacked conducting molecular planes with a spacing of 4.1 Å (Figures 8(c) and (d)). It is expected that the promotion of spiral morphogenesis based on steric hindrance of chiral functional groups is dependent on the enhancement of the molecular mobility at the air/water interface. Therefore, the formation of nanofibers was studied at different subphase temperatures (Figure 9). It is seen that an increase in the subphase temperature results in an increase in the diameter of the fibers, rather than the formation of the helical structure, which could be due to an increase in the aggregation force between the molecules. The diameters of the nanofibers formed at 15, 20, and 25°C, are 70, 125, and 190 nm, respectively. From the π–A curves, these correspond to aggregates of 20–40 molecules at 15°C, 30–60 molecules at 20°C, and 50–90 molecules at 25°C. The nanofiber morphology was retained upon inclusion of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) acceptor molecules to this system at a molecular ratio of 1:1 (Figure 10). Since F4-TCNQ is not amphiphilic, mixing it with the TTF derivative results in the formation of a charge transfer (CT) complex and interfacial nanofiber films. The retention of the nanofiber morphology after the inclusion of F4-TCNQ is because the structural formation is related to the stacking arrangement of the TTF molecular planes, and first-order spontaneous growth of mesoscopic nanofibers. The CT complex exhibited a broad absorption band in the IR region (2500–3500 cm−1), which was attributed to a CT between the electron-donating TTF and the electron-accepting F4-TCNQ moieties [39–41]. Figure 10 shows the color change of the solution to support the CT complex formation, and further, the AFM image and in-plane XRD profile also show evidences of maintaining of a mesoscopic fiber form and stacking of a conductive molecular plane. In addition, Figure 10(c) also shows UV spectrum of charge transfer complex of TTF-4Bor:F4-TCNQ = 1:1 in solution. Absorption band near 300 nm corresponds to the TTF-4Bor, and the band of 400 nm except the shoulder peak corresponding to F4-TCNQ. Absorption band at 700–800 nm corresponds to the anionic radical of the F4-TCNQ, and shoulder-shaped absorption band around 400 nm corresponds to the cationic radical of TTF . From the above, the formation of a charge-transfer complex in solution is supported.
As detailed in this chapter, the amphiphilic TTF derivative with chiral borneol groups are closely packed in the nanofiber morphology at the air/water interface. Although the densely packed molecular arrangement is easily attained by standard film fabrication methods at high surface pressures, mesoscopic nanofiber morphology is obtained by spontaneous one-dimensional growth at the air/water interface (Figure 11). The dense stacking structure of these molecular planes induces electrical conduction, and nanofibrous morphogenesis can be deployed in quantum devices, medical applications, etc. It can be seen that the control of the mesoscopic morphology at the air/water interface provides several variations and possibilities in the chapter of molecular organization, such as helical morphogenesis and size control of nanofibers .
In this chapter, monolayer behavior on the surface of water, mesoscopic morphological formation, and molecular arrangement in LB multilayers of the conductive TTF derivative with chiral groups were investigated. For this purpose, π–A isotherms, in-plane and out-of-plane XRD, and AFM measurements were carried out. From the AFM analysis, the formation of submicron networks and nanofiber morphology of the conducting molecular organization was confirmed at different monolayer compression rates. The in-plane and out-of-plane XRD measurements elucidated the formation of highly ordered layered structures and close-stacking of molecular planes due to π–π interactions.
Nanofibers of the TTF derivative were obtained by applying the one-dimensional growth method at low compression speeds and low surface pressure conditions. Under these conditions, the formation of helical nanofibers was also observed. These mesoscopic helical nanofibers, whose internal structure consists of stacked conducting planes, are expected to display spontaneous electrical conduction by electromagnetic induction. Hence, these materials are likely candidates for future innovation in the molecular device and healthcare industries.
2. Morphological control of crystalline nanofiber derived from amphiphilic diamide derivative which induces the thixotropic ability
In the molecular and materials chemistry, the concept of “hierarchy ” is very important. In usual, the molecular level orientation and arrangements beyond the level of mesoscopic morphogenesis cannot affect the level of the macroscopic physical properties. However, there are cases that molecular groups with crystalline array achieved a fibrous growth by the cooperative phenomenon of molecules, and its network form occurs thixotropic ability . If this crystalline fiber network contacts to other medium and induces the increase of that viscosity, the corresponding molecule is acting as a thixotropic agent beyond the size hierarchy of materials.
In addition, current nanotechnology in the chemistry and biophysics fields has undergone a remarkable development through the “discovery of the nanosized architecture” such as carbon nanotubes , “their deployment to the nanocomposite materials [45–48]”, and “re-attention to the bottom-up technologies as the classical LB method ”. Performance enhancement of analytical techniques, such as scanning probe microscopy and X-ray diffraction, has also helped strongly to the development of nanoscience.
By the way, the thixotropic phenomenon, which solidification and the flow are, respectively, occurred by standing and application of an external forces, is observed in familiar mayonnaise, ketchup, etc. Commercially available anti-sedimentation agent and liquid dripping inhibitors are also used as thixotropic agents. In addition, an additive which can be solidified the cooking waste oil and discarded it as a solid is also corresponding to a thixotropic agent. Traditionally, the main raw material of the thixotropic agent was 12-hydroxystearic acid. In this case, an occurrence origin of thixotropic properties is the fiber growth by 12-hydroxystearic acid molecule at micrometer level. The increase in viscosity has occurred by the contact of this developed microfiber to the corresponding medium. In other words, relationship between fiber growth and occurrence of thixotropic properties is almost equal. However, although the 12-hydroxy stearic acid can form a fibrous morphology in the view of molecular science, stearic acid does not form a fibrous form. It is well-known that stearic acid is the standard material of monolayer on the water surface, and corresponding LB film. Although stearic acid is a crystalline compound, its mesoscopic form is a sheet-like morphology. In other words, the influence of the hydrogen bonding between hydroxyl groups at the 12-position to the formation of the fibrous morphology is remarkable. However, the hydrogen bonding itself is also interaction at the molecular level. It cannot be asserted to affect the mesoscopic morphogenesis and macroscopic thixotropic by only the presence of a simple hydrogen bonding. However, hydrogen bonding “between biological polymers that forms the human body” and “between the polyamide fibers which is raw materials of a garment,” reality induces the macroscopic physical properties. In order to attain an understanding of these phenomena, the material evaluation by the hierarchical point of view will be essential by making full use of nano-technological analysis developed in recent years. In addition, discussion ability that be considered in connecting these phenomena will be extremely important. However, discussion to the 12-hydroxystearic acid itself has already been a thing of the past on the development of academic field of modern chemistry.
In the present chapter, amphiphilic diamide derivative which obtained by condensation reaction of 12-hydroxystearic acids and hexamethylenediamine was synthesized. The monolayer behavior, molecular arrangement, and surface morphology of organized molecular films of diamide derivative with two hydrocarbons were investigated by analysis of the π–A isotherms, in-plane and out-of-plane XRD profiles, and AFM images. Further, morphogenesis was encouraged by applying the epitaxial growth to a spin-cast film of diamide derivative. The form of the nanofibers thus obtained was indicated the linearly developed shape. Since the internal structure of the mesoscopic nanofiber is comprised of packed hydrocarbons at a molecular level, effective molecular packing is expected along the fiber growing direction.
2.2. Experimental section
2.2.1. Synthesis and characterization of amphiphilic diamide derivative with two hydrocarbons
In order to obtain the material used in this chapter, a condensation reaction of 12-hydroxystearic acid and hexamethylenediamine (2 mol: 1 mol) was performed. The obtained material was purified by recrystallization, and a removal of impurity checked by thermal analysis. Figure 12(a) shows thermogravimetric (TG) curves of this material under the N2 purge and in the air atmosphere. Under the N2 purge and in the air atmosphere, the decreasing of weight of material is started at 250 and 350°C, respectively. Further, there is a residual of heated material until 500°C and in the air atmosphere. That is to say, this material decomposes like a certain polymer at 250°C and do not sublimate as substance with low molecular weight. In other words, it finds that this compound is an extreme high heat resistance by the influence of hydrogen bonding. Figure 12(b) shows differential scanning calorimetric (DSC) thermogram of diamide derivative with two hydrocarbons. Only one transition peaks in both heating and cooling processes exist at around 150 and 135°C, respectively. In the case of unpurified sample, transition peaks of reacted substances in heating process are indicated at around 77 and 42°C. Therefore, it was considered that unreacted 12-hydroxystearic acid and hexamethylenediamine have been removed by recrystallization purification.
2.2.2. Characterization of bulk and their spin-cast film
The spin-cast films of diamide derivative with two hydrocarbons and the mixture with organo-modified layered silicate were formed from xylene– ethanol (9/1, v/v) mixed solution over 100°C. Organo-modified montmorillonite (MMT) was fabricated by surface modification method with natural MMT and long-chain quaternary ammonium cation at oil/water interface . Powder X-ray diffraction (XRD) measurement to the both bulk and cast film samples is performed by X-ray diffractometer (Rigaku, Rint-Ultima III, CuKα radiation, 40 kV, 30 mA) equipped with a graphite monochromator. Infrared (IR) spectra of the sample are measured by IR spectrometer (Bruker AXS TENSOR II).
2.2.3. Formation of monolayers of diamide derivative with two hydrocarbons on the water surface
Monolayers were formed by spreading from a CHCl3 solution including a small amount of trifluoroacetic acid (TFA) of diamide derivate having two-stearic chains with –OH groups (∼1.0 × 10−4 M) on the surface of distilled water (resistivity: approximately 18.2 MΩ cm). After evaporation of the CHCl3 for 5 min, surface pressure-area (π–A) isotherms were recorded at compression speeds ranging from 4.8 cm2 min−1. The air/water interface was kept at a constant temperature of 3.5, 12, and 15°C by circulation of thermostated water around the trough. Measurement of the monolayer properties and LB film transfer were carried out in a USI-3-22 Teflon-coated LB trough (USI Instruments). Further, mixed monolayers on the aqueous buffer solution including Na+ ion of diamide derivative and organo-MMT have been formed by co-spreading method of CHCl3 solution with small amount of TFA and toluene solution, respectively.
2.2.4. Study of the surface morphology and estimation of the molecular arrangement
The surface morphologies of the transferred films were observed using a scanning probe microscope (Atomic Force Microscopy, SII Nanotechnology, SPA300 with SPI-3800 probe station), and microfabricated rectangular Si cantilevers with integrated pyramidal tips, by applying a constant force of 1.4 N m−1. In this chapter, AFM observations were carried out in the tapping mode. XRD samples were transferred onto a glass substrate by the LB method (20 layers, subphase temperature of 15°C, and surface pressures of 35 mN m−1). The large spacing between the layers in the films was measured using an out-of-plane X-ray diffractometer (Rigaku, Rint-Ultima III, CuKα radiation, 40 kV, 30 mA) equipped with a graphite monochromator. The in-plane spacing of the two-dimensional lattice of the films was determined using an X-ray diffractometer with different geometrical arrangements [31, 32] (Bruker AXS, MXP-BX, CuKα radiation, 40 kV, 40 mA, a customized instrument) and equipped with a parabolic graded multilayer mirror. The X-rays were incident at an angle of 0.2°, and the films were scanned at a speed of 0.05°/20 s, as a result of which the in-plane XRD measurements had monomolecular resolution.
2.3. Results and discussion
2.3.1. Molecular arrangement and packing of diamide derivative including two-stearic chains with –OH groups
Figures 13(a) and (b) shows the powder XRD profiles and IR spectrum of diamide derivative with two hydrocarbons in bulk. In powder XRD profile, the developed layer spacing is indicated in low angle side. In this case, the long spacing peaks until fifth-order reflection are clearly confirmed. Furthermore, bands of stretching vibration of N–H and O–H are shifted to relative low angle side in IR spectra by the influence on the hydrogen bonding. In addition, amide I and II bands are clearly confirmed at around 1640 and 1550 cm−1.
Figure 14 shows the schematic illustration of two kind of possibility of molecular arrangement of diamide derivative with two hydrocarbons in bulk. In the case of model in Figure 14(a), molecules form the extended chain conformation. On the other hand, bilayer structure is formed like a general surfactant molecules in Figure 14(b). In both case, it finds that intermolecular hydrogen bonding between hydroxyl groups and amide groups have formed by the results of IR. There are two kinds of possibility of molecular orientation that first-order reflection corresponds to tilted single-layer spacing or bilayer spacing. In this stage, both possibilities cannot be rejected. However, authors support bilayer conformation as Figure 14(b) according to the nature of this type of amphiphilic materials.
2.3.2. Monolayer behavior and surface morphology of diamide derivative with two hydrocarbons
Figure 15 shows the π–A isotherms of monolayer on the water surface of a diamide derivative with two hydrocarbons at 3.5, 12, and 15°C. At 15°C, isotherm of diamide derivative with two hydrocarbons indicates the overshoot shoulder and plateau region near the 10 mN m−1. On the other hand, the number of two-dimensional phase transition increases in isotherms below 12°C. The origin of these two-dimensional phase transition can be inferred by the AFM measurement to monolayers which are transferred on the solid substrate. Figure 16 shows the AFM images of LB monolayers of diamide derivative with two hydrocarbons (Z-type) on mica, transferred at 7, 10 and 35 mN m−1. At low surface pressures region after first transition, continuously dotted nanodomains are observed. Next, thin fibrous morphology is confirmed after the second transition. Finally, in the high pressure regions, the developed fiber is formed as their monolayer feature. Therefore, it finds that an each two-dimensional transitions are corresponds to morphological changes of monolayer of diamide derivative with two hydrocarbons.
2.3.3. Molecular arrangement in organized molecular films of diamide derivative having two hydrocarbons
In order to estimate the crystallinity and periodicity of the molecules in multilayers of diamide derivative having two hydrocarbons, out-of-plane and in-plane XRD analyses of LB multilayers were carried out. Figures 17(a) and (b) shows the out-of-plane XRD profiles for LB multilayers (20 layers) which are transferred at 35 mN m−1. In the multilayers fabricated under high surface pressure conditions, it seems that a layer spacing along the
2.3.4. Liner morphological growth of nanofibers in a spin-cast film of diamide derivative having two hydrocarbons from layered silicate
At present, there are limitations in the ability to achieve one-dimensional growth of a nanofiber consisting of tightly packed molecules. Although the packed molecules are obtained in the two-dimensional interfacial film at high surface pressures, morphologies at the mesoscopic scale are too entangled and undulated due to the strong forces of aggregation, with the presence of long-range order between molecules, as a result of the competitive effect of van der Waals interactions and hydrogen bonding. Hence, if formation of the packed molecular arrangement is accelerated by the external forces at molecular level, the mesoscopic fiber growth might be linearly and hierarchically developed. In this chapter, the technique of epitaxial growth from harmless layered material in the mesoscopic spin-cast film was adopted, which used general organic solvent with relative low harmful effect at high temperature, inducing a spontaneous growth structure at the interface. Figure 19(a) and (b) shows AFM images of spin-cast film of diamide derivative and their composite with 1 wt% organo-modified MMT, respectively. From the comparison between these figures, it is confirmed that essential entanglement and wavy fibers have been performed the one-dimensional growth and changed to the linear shape in the spin-cast film by organo-MMT addition. As shown the results of XRD of Figure 20 in the Supporting Information, a organo-MMT is also the developed layer-organization with 38 Å double-layered period . Here, it will consider the interaction between organo-modified MMT and two-chain-type diamide derivative.
Figure 21(a) indicates the π–A isotherms of the mixed monolayer of two-chain-type diamide derivative: organo-modified MMT = 3:1 and 1:1. Compared to behavior of an each original monolayers, since a change in the collapsed surface pressure occurs, it can be understood the existence of interaction between components. In AFM observation to this mixed monolayer transferred on solid substrate, the fibers of diamide derivative are in contact with the organo-MMT without phase separation, which can be understood to be a system of an ideal mixing (Figure 21(b)). Next, the results of XRD of spin-cast films of Figure 19 are shown (Figure 22(a)). (Here, since the presence of the organo-MMT is a very small amount, they are not observed as the IR signal and this spectrum indicates very similar features to that in bulk as shown the IR result of Figure 23 in the Supporting Information.) From the comparison between both profiles, it finds that the third-order reflection has appeared and the intensity of the second-order reflection slightly decreased by organo-MMT addition. Considering from the concept of odd–even effect of high-order reflection, it seems that “an expression of the higher-order reflection” and “the occurrence of odd–even tendency” indicate an enhancement of regularity (Figure 22(b)). As the supporting of this speculation, the intensity of out-of-plane XRD profile of diamide derivative–organo-clay = 1:1 mixed multilayers clearly is increased to the one of the film of single diamide derivative, which is based on the enhancement of regularity along the
In this chapter, monolayer behavior on the water surface, mesoscopic morphological formation, and molecular arrangement in LB multilayers of the diamide derivative having two hydrocarbons were investigated. For this purpose, π–A isotherms, in-plane and out-of-plane XRD, and AFM measurements were carried out. From the AFM analysis, the formation of nanofiber morphology of the thixotropic molecular organization was confirmed at different surface pressures. The in-plane and out-of-plane XRD measurements elucidated the formation of highly ordered layered structures and close-packing of molecular chains due to van der Waals interaction.
Nanofibers of the two-chain-type diamide derivative were obtained by applying the epitaxial growth method in spin-cast film. Under these conditions, the formation of linearly developed nanofibers was also observed. These mesoscopic extended nanofibers, whose internal structure consists of the packed long-alkyl chain, are expected to display cooperative thixotropic ability by fiber growth. Hence, these materials are likely candidates for future innovation in an additive, waste oil treatment agent, and paint industries.
The authors greatly appreciate Mr. Eiichi Sato, Kusumoto Chemicals Ltd., and Dr. Yoko Tatewaki, Tokyo University of Agriculture and Technology for their kind providing of samples. The authors also thank Mr. Kyohei Ohmura and Mr. Takahiro Kikkawa, Saitama University for his kind help of data analysis.
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